1. Field of the Invention
The present invention relates to a manufacturing method and a manufacturing device of a sub-muffler outer cylinder, and more particularly, to a manufacturing method and a manufacturing device of a sub-muffler outer cylinder to form a cylindrical-shaped body having a polygonal cross-sectional shape.
2. Description of Related Art
A tapered cylindrical-shaped body may be manufactured by bending a trapezoidal plate shape workpiece or a fan plate shape workpiece. In a process of bending the workpiece, a roll bending method is used, for example.
For example, Japanese Unexamined Patent Application Publication No. 2012-236207 discloses a roll bending method using three truncated cone-shaped rolls. By pushing a push roll toward two receive rolls while allowing a plate-shaped workpiece to pass between the push roll and the two receive rolls, it is possible to bend the workpiece to obtain a cone-cylinder shaped formed product having a predetermined taper angle. By performing a predetermined process on such a cone-cylinder shaped formed product, this product can be used, for example, as a sub-muffler outer cylinder used for a vehicle.